Frequency dividing electrical circuit



April 16, 1957 Y. LACY 2,739,217

FREQUENCY DIVIDING ELECTRICAL CIRCUIT Original Filed Feb. 28, 19467'TORNEV United States Patent FREQUENCY DIVIDING ELECTRICAL CIRCUITLester Y. Lacy, Kansas, 111., assignor to Bell Telephone Laboratories,Incorporated, New York, N. Y., a corporation of New York Originalapplication February 28, 1946, Serial No. 650,977, now Patent No.2,573,150, dated October 30, 1951. Divided and this application August3, 1951, Serial No. 240,227

1 Claim. (Cl. 250-27) This is a division of application Serial No.650,977, filed February 28, 1946, now United States Patent No.2,573,150, October 30, 1951, .for Electrical Circuit.

The present invention relates to circuit means employing electrondischarge devices for transmitting current pulses and relates especiallyto such circuit means capable of transmitting pulses having a wide rangeof frequency, with stability and reliability.

In another aspect, the invention relates to an improved form offrequency dividing circuit of the so-called bucket and dipper type inwhich charges on a small condenser are transferred to a large condenseruntil a certain value of charge is built up on the latter which thendischarges into a load circuit. The improvements according to theinvention relate to means forequalizing the steps by which the charge isbuilt up on the large condenser; they further relate to the dischargingcircuit for the large condenser. These improvements aim to increase therange of frequencies over which the circuit satisfactorily operates andalso increase the range of division ratios and aid in adjusting todifferent ratios.

The nature and objects of the invention will appear more fully from thefollowing detailed description of the illustrative embodiment shown inthe drawing, in which:

Fig. 1 is a schematic circuit incorporating the invention and Fig. 2shows graphs of wave forms explanatory of functions to be described inconnection with Fig. l.

The bucket and dipper method of frequency division can be made clearfrom considering the part of Fig. 1 rom source 1 up to and including thetwo condensers and 6 and diodes 7 and 8, all of this part of the circuitbeing known in the art. It is preferable to have a square pulse input atthe grid of tube 3 'and if these are not directly available they can beobtained from sine wave source 1 by using the type of coupling circuitsshown for the grids of pentode stages 2 and 3 employingcapacityresistance networks and series grid limiting resistors. In Fig.2, if the wave form at A of Fig. 1 is sinusoidal, a wave of square formB can be derived at the point designated B in Fig. 1. Each time theplate of tube 3 is driven positive, some current flows through condenser5 into condenser 6 through diode 8. When the plate of tube 3 becomesless positive, some current flows in the opposite direction throughcondenser 5 into the platecathode circuit of tube 3 in series with diode7 and through ground to point 12, but this has no effect on the chargeexisting on condenser 6 since diode 8 is nonconducting under theseconditions. In this way, successive increments of charge are accumulatedon condenser 6 as indicated by the idealized staircase curve C until acritical voltage is reached at which condenser 6 discharges into theload, producing a sharp pulse D at each discharge. The graphs are drawnin Fig. 2 to represent a division ratio of five between the frequency ofthe pulses in wave B and the frequency of the pulses D.

The purpose of the tube 9 is to at least partially equalize the steps atC by equalizing the amount of charge transferred each time intocondenser 6. Due to the rising 2,789,217 Patented Apr. 16, 1957 voltageon the ungrounded terminal of condenser 6 as its charge increases,smaller and smaller amounts of charge would be added to condenser 6 asits charge increases unless some compensating provision were made. Byuse of tube 9 whose grid is connected to the ungrounded terminal ofcondenser 6, it is possible to make the volt-age at E increase at thesame rate as the voltage across condenser 6. The voltage at E isdetermined from a point on cathode resistor 11 of tube 9. As the gridpotential of tube 9 becomes more positive, more current flows throughresistor 11 raising the potential at E and a point on resistor 11 can befound by trial at which the potential at E attains the right value togive the desired compensation.

The operation of the tube 9 in equalizing the steps C will now beexplained by following through the circuit operation in greater detail.Assuming tube 3 to be a pentode as illustrated, the point H will vary inpotential between theextremes of plus 200 volts and practically zero(ground) in a time function represented by the B wave, assuming thevoltage of battery 4 to be 200 volts. Starting with condenser 6 fullydischarged and tube 3 conducting at step So, when tube 3 is cut off avoltage of approximately 200 volts is applied at H to the series branchconsisting of condenser 5, diode 8 and condenser 6, charging condensers5 and 6 in series and raising the voltage on condenser 6 to S1. Tube 9is so adjusted, as explained, that the potential at point B is changedfrom voltage S0 to voltage S1 during the above interval. When thepotential at H goes to zero the charge assumed placed on condenser 5 iscompletely wiped out and a small reverse charge is placed on it from Eraising the potential at J to about S1, so that when pointH again goespositive, the potential at joint I now starts to rise not from So asbefore but from S1. The result is that when condensers 5 and 6 arecharged by the increase in potential of 200 volts at point H the voltageacross condenser 6 increases from S1 to S2 and this increase is the sameas that from So to S1. This process continues through the other steps ofthe wave C. Another way of stating the action is that the quantity ofelectricity transferred is the same for each step.

As noted, curve C has been drawn with perfectly square corners on thesteps and with the steps exactly equal, both of which are idealized. Inpractice the corners would be rounded although by using seriesresistance at 30 the sharpness of the corners can be increased. Forfrequency dividing purposes the steps need have only a required degreeof equality and the use of tube 9 enables an approach to equality to berealized.

In accordance with one improvement feature of this invention a non-ohmiccurrent-dependent resistor 10 is inserted between resistor 11 and thecathode of tube 9 to increase the negative grid bias of tube 9 in thelow cathode current condition when the charge on condenser 6 is low andto reduce gradually this bias as the current through the tube increases.This prevents charging condenser 6 by a type of false operation due toinitial current fiow around the series loop including diodes 7 and 8,condenser 6 and resistor 11, which might occur if the potential at Ewere even slightly more positive than the upper plate of condenser 6.This condition can further be guarded against by use of a small battery22 poled to apply a negative voltage to E. As the cathode-ground currentof tube 9 increases, the resistance of element 10 decreases allowing agreater proportion of the potential drop in the external circuit of tube9 to appear across resistor 11. The element 10 may, for example, be apiece of the material known to the trade as thyrite. Varistor 10,therefore, acts similarly to a negative bias battery in the grid lead oftube 9. The use of 'a battery at this point has the disadvantage that itmust be in an uncluding thecase where the negative grid battery is used.A further feature of? the invention-comprises the' dis chargingcircuit'for the condenser 6,. includingthe tubes 15 and I4. This circuitin and offitself is a known type of flip-flop circuit having' a wide.frequency range of operation; By not depending upon a. timeconstantfcircuit While in .its: stable limiting condition, use of thiscircuit avoids the tendency to give a falseifidication when the inputfrequency changesio anew value.

' Considering. the discharge circuit, thecircuit is at rest aud'isstable in the condition where tuhe 1 4' is conducting "and tube, 13 isnon-conducting, Tuhe 14 has. no plate l'oad resistor so thatits cathode.is at relatively high positive potential due to the current flow throughresister 18. The cathode of tube. 13 is also: positive, its potentialbeingadiustable. by the-tap 19} on resistor 18, As the voltage builds upon condenser 6 it reachesthe critical. point atwliich tube 13 Begins, totransmit. Due to theflarge plate load resistor 20 the potential of theplate fall's andidrives the grid oftube14 negative, through the couplingcondenser. 15. The current inv resistor '18. now momentarily decreases.because ofthe falllnggofi of current through tube 14 and'becau'seof'thelimitingeiiect of resistor 29 on the plate. current of tube 13.This action builds itself up until'plate current is mostly cut oti. in.tube 14. The potential of both cathodes falls tonear ground andcondenser 6 dischargesv through the grid-cathode'circuit of tuhe 1-3.

After the condenser 6 has-discharged in. this manner, the circuitquickly returns to its.c.onditiono stability for at. the momentofcornplete discharge of'condenser-6both cathodes are at substantiallyground potential while the right-hand .plate of condenser, 15 has beencarried to-a potential well below ground; e. g., to -50 volts, by thedrop of potential'of' the plate of tube 13. This sends current throughgrid. leak. resistor. 16 in a direction. to raise the potential of thegrid of tube 14 and this. tube beginsto draw current raising thepotential. of the cath-.

ode of tube 13 relative to. itsgrid and reducing the current flowthrough that tube. This..'action is cumulative and results inreestablishing the. stable condition.

*While the flip-flop circuit itself it old,,-itsuse-as.a.sdischargecircuit for condenser 6 is believedv new. and has important advantages,the mainv one of which. isthe one mentioned above, namely, greaterstability against false indication when the input frequency changes.vThe circuit also has the advantage of simplicity and ease ofadjustmentto different frequency dividing ratios 7 The ratio of divisionof frequency can be varied by varying the slider 19 on resistor 18,since this determines the critical voltage at which condenser 6 willdischarge through the grid of tube 13'.

If the. input. driving wave should gootf and'therr after a time come onagain the circuit will restart exactly in step and give the properdivision of frequency. Even if the input goes Oh for a relatively longtime, the circuit ifs-14 will not send a false pulse into the load 21for it will remain in its: stable quiescent condition indefinitely. Fonthissa-me reason the circuit will faithfully divide an input frequencyof any Value withinxa' wide range.

What is claimed is:

A trigger circuit capable of responding to a Wide range of frequenciescomprising a pair of electron discharge devices. each including cathodemeans anda. gridandan anode, a condenser having-,means for. repeatedlycharging the san1e,,av circuit for. discharging saidcondenserac ross thegrid-cathode space of. the first. of: said devices upon 'the voltageacross said condenser. reaching a given critical value, said'cath'ode.means. having a. common connection to. an external terminal, said.common connection including a resistance in series with. said cathodemeans of the second of said devices,.means for includinga portion onlyof saidlresistance. in. series with said cathode means of saidfirstdevice inthe discharging circuit of. said. condenser, said resistance.portion. being common to saidcathode means of. said pair of. devices, aload circuit connected between. said. cathode. mcansof said. seconddevice, and said external terminal and thereby across said resistance,anode voltage. supply'means for both of said anodes, a large resistanceconnected between said supply and the anode. of. said first device only,and a couplingfcoudenser from.- the. 'anode of said first 'device to thegrid of saidsecond device.

References Cited in the file of this patent Y

